The native peptide GPHRSTPESRAAV (60518-1) is a part of the hydrophilic loop domain of presenilin 1 that is selectively recognized by GSK-3b. The sequence is not recognized by p38a, p38b, PKC, or CK II.
Hirata, Y. et al. Mol. Biol. Cell 14, 302 (2003); Kirschenbaum, F. et al. J. Biol. Chem. 276, 7366 (2001).